kern/45355: Reader/writer lock error: rw_vector_enter: locking against myself

[apb%cequrux.com@localhost]

>Number:         45355
>Category:       kern
>Synopsis:       Reader/writer lock error:  rw_vector_enter: locking against 
>myself
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Sep 10 16:30:00 +0000 2011
>Originator:     Alan Barrett
>Release:        NetBSD 5.99.55
>Organization:
Not much
>Environment:
System: NetBSD i386 5.99.55 (sources from 2011-09-02 14:00 UTC)
Architecture: i386
Machine: i386
>Description:
The system crashes frequently (more than once per day).  I am usually
not able to get any debug information, because after a crash pressing
alt-control-F1 does not switch the display from graphics to text mode.
The most recent crash was while I was using a text console, so I was
able to get the following information.  (This is transcribed from blurry
photos, and it's likely that there's confusion between the digits
0 and 8.)

Reader / writer lock error: rw_vector_enter: locking against myself

lock address : 0x00000000d483e0b0
current cpu  :                  0
current lwp  : 0x00000000d8eac2a0
owner/count  : 0x00000000d8eac2a0 flags    = 0x0000000000000004

panic: lock error
fatal breakpoint trap in supervisor mode
trap type 1 code 0 eip c0251254 cs 8 eflags 206 cr2 ce881000 ilevel 0
stopped in pid 15882.1 (vim) at netbsd:breakpoint+0x4: popl %ebp

db{0}> bt
breakpoint ...
panic ...
lockdebug_abort ...
rw_abort ...
rw_vector_enter ...
genfs_lock ...
layer_bypass ...
VOP_LOCK ...
vclean ...
getcleanvnode ...
getnewvnode ...
ffs_vget ...
ffs_valloc ...
ufs_makeinode ...
ufs_create ...
VOP_CREATE ...
vn_open ...
sys_open ...
syscall ...

>How-To-Repeat:
The crash happened as I was attempting to save a file from the
"vim" editor (installed from pkgsrc).  The file system is
ffs+wapbl on cgd.  The file system also happens to be the
backing layer for a read-only nullfs mount, and it's possible that
a process was attempting to access the same file through the
read-only nullfs mount at the same time as the editor was
attempting to save the file to the writabe backing layer.

>Fix: